I have an HTC Droid Incredible running Android 2.2 FroYo and would like to use custom sounds/songs as ringtones for text message notifications, event and task reminders, Facebook and Twitter notifications, and email messages. I have the MP3s that I want to use located in the /ringtones directory of my phone, but they don't show up on the list of possible sound effects/tones/notifications, but they do show up in the selection for incoming call ringtones. What do I do to use them?

To do this you need to create a folder called "notifications" on the root of your SD. You could mount your device to do this or use an application "Astrow" either way, Put your MP3 files here and you can use them as Notification sounds as well as ringtones.

To set up your mp3 file as a ringtone, simply create a new folder on your SD Card and rename it "ringtones", without the quotes of course. (Do same for alarms, notifications and ui). After that, add your mp3 files to the folder. Go to "Setting--sound--phone ringtone", there, you will see your added mp3 file.